Wireless terminal such as mobile phone comprises RF (Radio Frequency) a signal line. The RF signal line is normally made of coaxial cable. Such RF signal line made of coaxial cable makes an inner space of the wireless terminal narrower so that a flexible circuit board generally applied to the wireless terminal nowadays.
However, traditional flexible circuit board is apt to be fractured or broken down in the part of bending such as folding type wireless terminal.
The flexible circuit board makes sure of the necessary amount of signals by decreasing line loss at signal transmission through thickening the signal line or increasing the size of signal line, and by decreasing the signal loss of reflection through shielding the external signals from outside.
The flexible circuit board has optimum impedance of about 33Ω at the signal transmitter, and optimum impedance of about 75Ω at the signal receiver. Considering both the transmitter and receiver, it is ordinary that the flexible circuit board should be designed to have characteristic impedance of about 50Ω.
In the case that external signals are introduced from the other components, the characteristic impedance would be deviated from the normal level of 50Ω, so that the signal transmission efficiency might be aggravated. Particularly, when any components such as a main board, a sub-board, and a battery are brought into contact with or disposed close to the ground, the characteristic impedance of the flexible circuit board deviates from about 50Ω thereof.
Therefore, the flexible circuit board should be applied at the reasonably separated location from other components so as to prevent unwanted impedance variation. In this case, however, the inner space of the terminal, which is the main merit and advantage of flexible circuit board, may be narrower.
The flexible circuit board may be placed near other components by the impedance matching. However, in this case, the shape of flexible circuit board should be changed as well, according to the variation of shape or location of at least one component among its main board, sub board, battery or so. Therefore, it is necessary that the flexible circuit board can be installed freely inside of the wireless terminal without effect of other components therein.
The background described herein will be understood only for the purposes of understanding of background of the invention, so that said background should not be accepted the prior art of the invention in the view of the person having ordinary skilled in the art.